So, I made an emoji URL shortener with Rust and shared it in some places including the Rust community. And oh man this is the first thing I made that got this many visitors which is pretty nice knowing that people were curious enough to try it despite them probably feeling disgusted from me bringing such a thing to existence.

Some glowing ✨ reviews:

“Thanks, I hate it.” – Pay08, 2022

“downvoted for being a menace to society.” – MultiplyAccumulate, 2022

“blursed " – Jaxius3

““Made with regret.” Hahahaha. Excellent.” – IronWhiskers, 2022

“What is wrong with you?” – Jeff

That’s a lot of people disgusted by what I made

That’s a lot of people disgusted by what I made

Here are some of the things I learned from building a simple project.

Tech Stack

After looking around, I decided to go with the following:

  • axum (web server)
  • maud (HTML templates via Rust macros)
  • postgres (persistent data storage and business logic)
  • sqitch (database schema migration tool)
  • typescript (you know what this is)
  • docker (“simple” deploys)
  • nix (reproducible environments)

PostgreSQL Procedures

Procedures are extremely cool although this isn’t exactly new to me. I’ve been experimenting with this in one of my previous, unfinished projects called GNAWEX 1 (One day I will finish it don’t you worry).

This allows you to implement some business logic in SQL, without having to implement it in the application level. If ever PostgreSQL is a constant in your project, and intend to rewrite the app from scratch, you might just end up having to rewrite the glue rather than your business logic. emojied isn’t doing anything too exciting though, so I can’t really demonstrate all that is cool about it.

Okay, an example would be fetching a URL given an identifier, and incrementing the clicks column by one. Here’s an example of a procedure that does exactly that:

CREATE FUNCTION app.get_url(query TEXT)
                          -- ^ This contains the emoji sequence `identifier`
  RETURNS TEXT
  LANGUAGE sql
  AS $$
    -- Considered as a "clicked" link whenever this gets triggered
    UPDATE app.links
      SET clicks = clicks + 1
      WHERE links.identifier = $1;

    -- Builds the URL so that I don't have to do this in the web server
    SELECT concat(scheme, '://', hosts.name, path) AS url
      FROM app.links
      JOIN app.hosts
      ON links.host = hosts.host_id
      WHERE links.identifier = $1;
  $$;

It’s a simple function that uses SQL as the language that expects any TEXT, and returns a TEXT as well, which is a sequence of emojis, and the URL it maps to respectively. Since whatever happens in this procedure is in the same transaction as what called it, e.g (SELECT * FROM app.get_url('🍊🌐')), if any of this fails, then it rolls back everything, including the incrementing of clicks. If this was at the application level, I’d have to reach for whatever transaction implementation it uses (like Ecto.Multi) which doesn’t make sense in this case cause Postgres already natively supports transactions.

I try to make heavy use of stored procedures as long as it’s applicable. Inserting to multiple tables with one function, fetching leaderboard entries, etc.

Error handling with implicit From<T>

Error handling is pretty nice with Rust, especially since I was never a fan of exceptions since it made control flow so weird. Although that may be because I never really invested that much time working with them. In Rust, I like that you can do two things for errors: errors encoded as ADTs, or panic (unrecoverable). Although I’m not entirely sure if all errors can be encoded in sum types, and what can be done if ever one needs to recover from a panic. But for emojied, I definitely don’t have to think about that.

What I did have to deal with was finding a more convenient way when dealing with other Error types. For instance, there’s tokio_postgres::Error, then there’s env::VarError, and if I need to bubble up these errors to the binary, I’m gonna need a convenient enough way to do that otherwise I’m gonna have a difficult time.

Let’s say I have two errors, a database one, and an application one.

enum AppError {
  Foo,
  Baz
}

enum DbError {
    FailedToConnect,
    InvalidTLSCert
}

fn some_db_action() -> Result<String, DbError> {
    Err(DbError::FailedToConnect)
}

fn some_app_action() -> Result<String, AppError> {
    let result1 = some_db_action()?;
    let result2 = some_db_action()?;

    Ok(result1)
}

This fails to compile, here’s what rustc says:

error[E0277]: `?` couldn't convert the error to `AppError`
    |
212 | fn app_action() -> Result<String, AppError> {
    |                    ------------------------ expected `AppError` because of this
213 |     let result1 = db_action()?;
214 |     let result2 = db_action()?;
    |                              ^ the trait `From<url::DbError>` is not implemented for `AppError`
    |
    = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `Fro
m` trait
    = note: required because of the requirements on the impl of `FromResidual<Result<Infallible, url::DbError>>`
 for `Result<std::string::String, AppError>`

For more information about this error, try `rustc --explain E0277`.

So it tells me that using ? implicitly converts DbError to AppError via the From trait. And because I do not have a trait instance like impl From<DbError> for AppError, it fails.

Another thing is I somehow need to bubble up DbError up to the application error somehow. The method I ended up using is to just add a field to the AppError record. It’s a bit tiring to copy all the DbError variants over to the AppError enum. I mean, it’s fine for this one since it doesn’t have that many, but it becomes.

enum AppError {
    DbError(DbError), // Hooray!
    Foo,
    Baz
}

And then I can create a From<DbError> instance:

impl From<DbError> for AppError {
    fn from(e: DbError) -> Self {
        AppError::DbError(e)
    }
}

Which compiles!

If I wanted to avoid From, I could do this:

let result1 = db_action().map_err(|_| AppError::Foo)?;

Except it’s kinda annoying cause I have to do this at every call site. Although there are times when I did end up using this.

Application configuration

While convenient, I can’t just hard-code everything into the application, especially for a public project. There are a lot of sensitive data like certs, and sometimes it’s just more convenient for whoever is using the application to change stuff without touching the source code. In my case, I had to make it flexible enough to change database credentials.

A common way to do it is through environment variables.

e.g PG__HOST="db.example.com" emojied. So whenever I need to update stuff, all I have to do is just change the environment variable, and I’m spared from touching the source code!

Here’s emojied’s config for it to run:

pub struct AppConfig {
    /// Application host
    pub host: String,

    /// PostgreSQL config
    pub pg: tokio_postgres::Config,

    /// Pool manager config
    pub manager: ManagerConfig,

    /// Pool size
    pub pool_size: usize,

    pub ca_cert_path: Option<String>,
}

Then I created an associated function for it called from_env/0 which returns a Result<AppConfig, Error>. I’ll talk about the Error part in the Error Handling section. Then I can use Rust’s std::env module to get a var’s value!

Here’s a tiny example:

use std::env;

struct AppConfig {
  pg_host: String,
}

impl AppConfig {
  fn from_env() -> Result<AppConfig, Error> {
      let host = env::var("PG__HOST")?;

      Ok(AppConfig { pg_host: host })
  }
}

Side note: This kinda looks monadic, where it binds AppConfig to host, and evaluates to Error and “exits” otherwise.

Handling database…handler in axum

I created this database handle that has all the things I need to communicate with the database server:

pub struct Handle {
    pub pool: Pool,
}

It’s pretty simple. It’s a struct that has a pool field. Then I created two more functions to make things more convenient: new/1, and client/1.

new(config: AppConfig) -> Result<Handle, Error> expects an AppConfig as an argument, and if all goes well, then a new database handle with all the important things in it. client(&self) -> Result<Pool, Error> expects a reference to self, which is Handle in this case. This uses the DB pool to create a new client. From this client, you can do DB queries with it.

// Grabs a client from the pool
let client = handle.client().await?;

// Runs a query that gets a URL's stats
let data = client
    .query("SELECT * FROM app.get_url_stats($1)", &[&identifier])
    .await?;

// Manually maps the row to a leaderboard entry
let db_id = data[0].try_get(0)?;
let db_clicks = data[0].try_get(1)?;
let db_url = data[0].try_get(2)?;

Ok(leaderboard::Entry {
    identifier: db_id,
    clicks: db_clicks,
    url: db_url,
})

Okay, so I somehow need access to the database handle in the “controllers”, like in controllers::leaderboard.

I’m only calling it a controller since it’s a common concept. axum doesn’t call it that.

let app = Router::new()
    .route("/leaderboard", routing::get(controllers::leaderboard));

axum recommends 2 mentions that you could use “request extensions” which looks like it acts like middleware. It recommends to have Arc inhabit Extension (Extension<Arc<T>>), but why?

Time to do it in some wrong ways. This is fine since rustc is quite helpful with its error messages.

I’ll try to move handle instead:

use axum::{extract::Extension, routing::get, Router};
use std::net::SocketAddr;

pub async fn run(handle: db::Handle) -> Result<(), hyper::Error> {
    let app = Router::new()
        .route("/leaderboard", routing::get(controllers::leaderboard))
        .layer(Extension(handle));
                      // ^ Here

    let addr = SocketAddr::from(([0, 0, 0, 0], 3000));

    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .with_graceful_shutdown(signal_shutdown())
        .await
}

Doing that gives me this error:

error[E0277]: the trait bound `db::Handle: Clone` is not satisfied
  --> src/lib.rs:36:16
   |
36 |         .layer(Extension(handle));
   |          ----- ^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `db::Handle`
   |          |
   |          required by a bound introduced by this call
   |
   = note: required because of the requirements on the impl of `tower_layer::Layer<Route<_>>` for `Extension<db::
Handle>`

For more information about this error, try `rustc --explain E0277`.

It seems like I need to derive Clone for db::Handle since it probably gets cloned every time, although I’m not sure exactly when it does get cloned. In every new request?

So what happens if I do derive Clone?

#[derive(Clone)]
struct Handle {
  pub pool: Pool
}

Then I need to make sure that the function’s type signature matches:

pub async fn leaderboard(
    Extension(handle): Extension<db::Handle>
 // ^ Here! axum seems to know exactly where to apply it to the args. Not sure
 // how this is done (yet).
) -> (StatusCode, Markup) {
    match leaderboard::fetch(&handle).await {
        Ok(entries) => {
            (StatusCode::OK, views::leaderboard::render(entries))
        },
        Err(_e) => (StatusCode::INTERNAL_SERVER_ERROR, maud::html! {}),
    }
}

Well, it seems to compile just fine. The leaderboard page works fine as well. I don’t really have that much experience with this yet but my current assumption is that I’m required to derive Clone for Handle since there’s no way to do shared ownership. So what it does is that it ends up cloning it every time. But, what if I don’t want to clone it? What if I just pass around references?

pub async fn run(handle: db::Handle) -> Result<(), hyper::Error> {
    let app = Router::new()
        .route("/leaderboard", routing::get(controllers::leaderboard))
        .layer(Extension(&handle));
                      // ^ Here

    let addr = SocketAddr::from(([0, 0, 0, 0], 3000));

    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .with_graceful_shutdown(signal_shutdown())
        .await

Compiles with this helpful error message:

error[E0597]: `handle` does not live long enough
  --> src/lib.rs:36:26
   |
22 |       let app = Router::new()
   |  _______________-
23 | |         .route("/leaderboard", routing::get(controllers::leaderboard))
24 | |         .layer(Extension(&handle));
   | |__________________________^^^^^^^_- argument requires that `handle` is borrowed for `'static`
   |                            |
   |                            borrowed value does not live long enough
...
44 |   }
   |   - `handle` dropped here while still borrowed

For more information about this error, try `rustc --explain E0597`.

Unfortunately, I’m not too familiar with how lifetimes work in async/await. But it looks like since it’s non-blocking, handle gets dropped since the function reaches the end of its scope while the server is still running.

This is all just somewhat smart guessing though. I’m gonna need to do more reading on this topic.

Wait, what about app then? Won’t this get dropped as well? I wanted to confirm if this did get moved, or if it did some other trickery I had no idea about:

    let app = Router::new()
        .route("/leaderboard", routing::get(controllers::leaderboard))
        .layer(Extension(handle));

    let addr = SocketAddr::from(([0, 0, 0, 0], 3000));

    let foo =
        axum::Server::bind(&addr)
            .serve(app.into_make_service())
            .with_graceful_shutdown(signal_shutdown())
            .await;

    println!("{:?}", app);

    foo

So if app does get moved, then rustc should complain about me accessing a variable with no ownership; which it does:

error[E0382]: borrow of moved value: `app`
   --> src/lib.rs:46:22
    |
22  |     let app = Router::new()
    |         --- move occurs because `app` has type `Router`, which does not implement the `Copy` trait
...
42  |             .serve(app.into_make_service())
    |                        ------------------- `app` moved due to this method call
...
46  |     println!("{:?}", app);
    |                      ^^^ value borrowed here after move
    |
note: this function takes ownership of the receiver `self`, which moves `app`

Phew! It’s almost like I’m encouraged to try out all the failed scenarios to learn a lot of things since the compiler is quite helpful.

Okay, since I didn’t want this to get cloned all the time, I will just follow what axum used in its examples - the usage of Arc<T>:

pub async fn run(handle: db::Handle) -> Result<(), hyper::Error> {
    let handle = Arc::new(handle);
    //  ^ Shadow previous binding with `Arc<db::Handle>`

    let app = Router::new()
        .route("/leaderboard", routing::get(controllers::leaderboard))
        .layer(Extension(handle));
                      // ^ Here

    let addr = SocketAddr::from(([0, 0, 0, 0], 3000));

    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .with_graceful_shutdown(signal_shutdown())
        .await
}

And then I’ll remove the Clone derivation:

pub struct Handle {
    pub pool: Pool,
}

So if I’m not mistaken, which I probably am, Arc<T> should allow me to share ownership of db::Handle without having to clone it 3.

pub async fn leaderboard(
    Extension(handle): Extension<Arc<db::Handle>>
) -> (StatusCode, Markup) {
    match leaderboard::fetch(&*handle).await {
        Ok(entries) => {
            (StatusCode::OK, views::leaderboard::render(entries))
        },
        Err(_e) => (StatusCode::INTERNAL_SERVER_ERROR, maud::html! {}),
    }
}

Then in leaderboard::fetch/1:

pub async fn fetch_url(
    handle: &db::Handle,
    identifier: String
) -> Result<String, Error> {
    let client = handle.client().await?;
    let row = client
        .query_one("SELECT app.get_url($1)", &[&identifier])
        .await?;

    row.try_get(0).map_err(|e| Error::from(e))
}

Although, I had to manually dereference it to get the reference to Handle. It’s also a good thing that I don’t have to mutate handle at all because otherwise this would’ve been a more painful experience.

Connecting to a managed database

Initially, I used sqlx as the db library since it gets recommended in almost every post about SQL libraries on the Rust subreddit. It worked fine for me until I had to get it to connect to DO’s managed DB. It required me to connect to it via TLS, and it wasn’t a pleasant experience trying to debug what’s wrong with sqlx, so I ditched it settled with tokio-postgres, deadpool-postgres, and native-tls. Oh, I also had a difficult time 4 with rustls since it didn’t seem to like DO’s CA certificate, which is why I settled with native-tls.

native-tls needed OpenSSL setup, which I was able to do with Nix (for the dev environment):

  # ...
        devShell = pkgs.mkShell {
          # inherit (self.checks.${system}.pre-commit-check) shellHook;

          buildInputs = with pkgs; [
            # Back-end
            pkgs.rustc
            pkgs.cargo

            pkgs.openssl
            pkgs.pkg-config
          ];

          PKG_CONFIG_PATH = "${pkgs.openssl.dev}/lib/pkgconfig";
        };

  # ...

So I had to provide the CA cert during runtime, not build-time since: 1) it’ll be easier to distribute the static binary and Docker image, and 2) some CA certs are only given during runtime (like DO if ever you’re using app platform). This was my process:

  1. Build static binary & image without CA certs and other DB secrets
  2. When the image runs, it’s assumed that the necessary environment variables, like one that contains the certificate contents, exist.
  3. Write the certificate contents to a file.
  4. Run emojied

This seems to be a pretty standard process, although this is fairly tedious.

// src/config.rs
use tokio_postgres::config::SslMode;

let mut pg_config = tokio_postgres::Config::new();

// I also read other PG values like hostname, DB name, user, etc. but excluded
// those for brevity.

// Not providing CA_CERT is fine
let ca_cert_path = match env::var("PG__CA_CERT") {
    Ok(path) => {
        // I think `Prefer` is fine as well, which is the default
        // for `tokio-postgres`.
        pg_config.ssl_mode(SslMode::Require);
        Some(path)
    },
    Err(_e) => {
        None
    }
};

I allowed it to continue running without the cert path in PG__CA_CERT for dev environments.

// Somewhere in src/db.rs

let manager = match app_config.ca_cert_path {
    Some(ca_cert_path) => {
        // Read file into byte vector
        let cert = std::fs::read(ca_cert_path)
            .map_err(|e| Error::CACertFileError(e))?;

        // Create a certificate from a PEM file
        let ntls_cert = Certificate::from_pem(&cert)
            .map_err(|_| Error::InvalidCACert)?;

        let tls = TlsConnector::builder()
            .add_root_certificate(ntls_cert)
            .build()
            .map_err(|_| Error::FailedToBuildTlsConnector)?;

        let conn = MakeTlsConnector::new(tls);

        Manager::from_config(app_config.pg, conn, app_config.manager)
    }
    None => Manager::from_config(app_config.pg, NoTls, app_config.manager),
};

// Since we need a `manager` to build a pool
let pool = Pool::builder(manager)
    .max_size(app_config.pool_size)
    .build()
    .map_err(|_| Error::FailedToBuildPool)?;

The process was quite similar with SQLx but there was something, that I don’t really remember anymore, which made it so frustrating to work with.

Unfortunately, DO doesn’t support multiline environment variables, for some reason, so cramming everything including the BEGIN CERTIFICATE and END CERTIFICATE into one line resulted in it getting rejected. So, I just got what’s in between, and manually appended it to the file instead.

echo "Dumping CA certificate to /app/ca-certificate.crt"
echo "-----BEGIN CERTIFICATE-----" > /app/ca-certificate.crt
echo $CA_CERT >> /app/ca-certificate.crt
echo "-----END CERTIFICATE-----" >> /app/ca-certificate.crt

echo "Executing emojied"

./emojied

Kind of hacky, and inconvenient especially if I forget. But it works!

URL redirect woes

This is a short one. For the redirect, I returned an HTTP status 301 5 with a response containing the URL to redirect to. So the process goes something like this:

  1. Enter https://emojied.net/🍊🌐 in the browser.
  2. emojied looks for an entry with 🍊🌐, and gets the associated URL.
  3. Respond with an HTTP 301 and the URL
  4. Browser automatically performs the redirect

Unfortunately, and I spent 30mins on this scratching my head why this was happening, the request would get cached, and this is bad! It’s bad because I had to increment the clicks column every time the link is visited. But if it’s cached, then the server won’t bother to call the functions it needs to call!

Then, I found out that 301 gets cached automatically by the browser 6, and that I needed to use 302.

HTML templating with maud

I had a pleasant experience with server-side templating while I was building a Haskell project called Swoogle. I used lucid 7 which was a pretty darn elegant HTML DSL.

-- Category options
select_
  [ id_ "category-options"
  , name_ "resource"
  , class_ "bg-white font-semibold dark:bg-su-dark-bg-alt text-su-fg dark:text-su-dark-fg"
  , required_ "required"
  ] $ do
  option_ [disabled_ "disabled", selected_ "selected", value_ ""] "Category"
  option_ [value_ "people"] "People"
  option_ [value_ "film"] "Film"
  option_ [value_ "starship"] "Starship"
  option_ [value_ "vehicle"] "Vehicle"
  option_ [value_ "species"] "Species"
  option_ [value_ "planet"] "Planet"

Well, I wanted something like that in Rust, and I found maud 8. I did run into a problem when I tried to use its latest version with axum since something must’ve changed in axum, so I had to pull from the main instead:

[dependencies]
...
maud = { git = "https://github.com/lambda-fairy/maud", branch = "main", features = ["axum"] }
...

So with this, I could do stuff like:

fn foo() -> Markup {
  html! {
    ("Hello")
    h1 class="text-red-500" { ("Hello!") }

    h2 class=("font-semibold") { ("Hey") }
  }
}

<noscript> tag, and problems with JS toggling extensions

I wanted to have the website work with JS disabled because, well, it was a very simple website. There was no reason why I couldn’t make all the important features work without JS!

So I ended up making heavy use of the <noscript> tag, since it allowed me to display alternative content when the browser has JS disabled. You’ll see it littered all over the codebase, like so:

@match data {
    RootData::Auto(_) => {
        noscript {
            div class="w-full sm:w-4/5 mt-2 mx-auto text-su-fg-1 dark:text-su-dark-fg-1" {
                a href="?custom_url=t" type="button" class="font-medium underline" {
                    "Custom URL"
                }
            }
        }
    }

    RootData::Custom(_) => {
        noscript {
            div class="w-full sm:w-4/5 mt-2 mx-auto text-su-fg-1 dark:text-su-dark-fg-1" {
                a href="/" type="button" class="font-medium underline" {
                    "Autogenerate a custom URL for me"
                }
            }
        }
    }
}

These only get rendered by the browser when JS is disabled. But what do browser extensions like NoScript when it “disables” JS? It’s something like this:

  1. Block requests for JS files via CSP (Content Security Policies)
  2. Replace noscript tags to span or div tags

The problem I ended up with was in #2. Why? Because the noscript tag attributes weren’t copied over to the new span/div tags. And that breaks a lot of stuff.

So while emojied does work without JS, it won’t work due to how the extensions work 9.

Conclusion

Alright, that was a lot. I did learn a lot from this experience. I actually only read until chapter 10 of the Rust Book, and skipped to some parts like advanced traits, and other things. I really like the fact that there’s a detailed book that talks about some idiomatic Rust patterns, and even the more advanced stuff, that’s completely FREE. How crazy is that? My wallet is spared!

I usually try to avoid failure, even in Haskell, cause its error messages are pretty bad. When I started out, it was pretty much worthless to read GHC’s error messages since it would just confuse me even more. It was only until I had people guide me (like justosophy, thank you) that I slowly got to understand what GHC was trying to tell me. With Rust though, it’s a completely different experience.

I like failing because Rust is very helpful with its error messages. In fact, I discover new things by reading it so I’m not punished for trying out different things that don’t work just to gain more insight.

I also like that it’s fairly easy on resources. I didn’t even bother optimizing this at all since I mostly have no idea what I’m doing, and I’m trying to avoid having to deal with lifetimes as much as possible. I’m hosting this on a 1x shared vCPU + 512MB RAM, and it didn’t break a sweat during peak load.

Anyway, so far, so good! I’m pretty ecstatic to continue learning Rust.


  1. https://github.com/gnawex/gnawex ↩︎

  2. https://docs.rs/axum/0.5.1/axum/#using-request-extensions ↩︎

  3. https://doc.rust-lang.org/std/sync/struct.Arc.html ↩︎

  4. https://old.reddit.com/r/rust/comments/txglob/need_help_regarding_deadpoolpostgres_rustls_and/ ↩︎

  5. https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/301 ↩︎

  6. https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching#targets_of_caching_operations ↩︎

  7. https://hackage.haskell.org/package/lucid ↩︎

  8. https://github.com/lambda-fairy/maud ↩︎

  9. https://github.com/hackademix/noscript/issues/238 ↩︎